Orthogonal Frequency Division Multiplex (OFDM) modulation techniques are often used to transmit signals in a network, such as, for example, cable networks, wireless networks or digital television broadcasts. These may including wireless personal area networks (WPAN), wireless local area networks (WLAN), Wireless Metropolitan Area Networks (WMAN), Wireless Wide Area Networks (WWAN), Digital Video Broadcasting (DVB-T2) and the like. To improve spectrum usage efficiency, these OFDM-based communication systems are increasingly being implemented as Single Frequency Networks (SFNs), where the same frequency is used by multiple transmitters to broadcast the same information over a large region. This can result in the reception of replicas of the signal at the receiver, where the replicas appear as echoes with relatively large time differences. These large time differences typically exceed the cyclic-prefix guard interval that is normally used to mitigate signal corruption associated with echo.
These SFN generated echoes create a cyclic ambiguity in the channel impulse response which adversely affects channel equalization and symbol timing recovery and thus degrades the OFDM receiver performance. Existing solutions to this problem rely on the use of continuous pilot carriers that occupy the same carrier location in every received OFDM symbol. There is an increasing trend, however, to reduce the number of continuous pilot carriers or, in some cases, eliminate them entirely since they use up spectrum that could be occupied by data carriers. Existing solutions relying on continuous pilot carriers would thus be rendered increasingly ineffective.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.